Hitherto, many agricultural and horticultural fungicides have been known. However, owing to problems with an effect, chemical resistance, safety, and the like, there is a need for a more effective chemical that can be more safely used.
Prumycin (4-N-D-alanyl-2,4-diamino-2,4-dideoxyarabinose) is known as a chemical having effects against gray mold, sclerotial disease, powdery mildew, and the like. Prumycin was isolated from a culture filtrate of a Streptomyces sp. strain F-1028 by Hata et al. in 1971 (Non Patent Literature 1), and later, in 1973, it was reported by Omura et al. that effects of prumycin were found against gray mold and sclerotial disease of beans, and cucumber powdery mildew (Non Patent Literature 2). The structure of prumycin was determined by Omura et al. in 1974 (Non Patent Literature 3). After that, three independent groups achieved total synthesis (Non Patent Literatures 4 to 13), and a structure represented by the following formula was identified.

With regard to naturally occurring prumycin, it was revealed that, besides the above-mentioned Streptomyces sp., a specific strain of Bacillus cereus produced prumycin (Patent Literature 1 and Non Patent Literature 14). Further, in 1989, it was reported that a specific strain of Bacillus subtilis produced prumycin (Patent Literature 2).
However, although its fundamental activity is high, prumycin has not yet been put into practical use owing to lack of effect in actual use. In order to solve the problem of lack of effect, its combined use with another chemical, that is, an iturin A-based peptide (Patent Literature 3) or benomyl (Patent Literature 4) has been considered, but all the same, has not yet been put into practical use owing to lack of effect.
Meanwhile, surfactin family members are also substances that have long been known. In 1968, K. Arima et al. isolated a substance having a high surface-active ability from a culture broth of B. subtilis, and named the substance surfactin (Non Patent Literature 15). The structure of surfactin was elucidated by A. Kakinuma et al. in 1969, and revealed to be, as shown in Table 1, a lipodepsipeptide structure formed of: a C13 to 17 β-hydroxy fatty acid whose terminal branching structure has any of iso, anteiso (hereinafter abbreviated as ai), and normal (hereinafter abbreviated as n) side-chain structures; and four molecules of Leu, and one molecule each of Val, Glu, and Asp (Non Patent Literature 16).
After that, as surfactin family members, [Ala4]surfactin (Non Patent Literature 17), [Leu4]surfactin (Non Patent Literature 18), [Ile4]surfactin (Non Patent Literature 18), and [Val7]surfactin (Non Patent Literature 19) were each isolated from a culture broth of B. subtilis and structurally determined. Further, [Ile7]surfactin (Non Patent Literatures 20 and 21) was isolated from a culture broth of each of B. licheniformis and B. amyloliquefaciens and structurally determined, and halobacillin (Non Patent Literature 22) and lichenysins A and G (Non Patent Literatures 23 and 24) were isolated from Bacillus sp. bacteria including B. licheniformis and structurally determined (Table 1).
TABLE 1 β-OH-fatty acid (carbonα-amino acidsnumber and 1234567structure)Surfac-GluLeuLeuValAspLeuLeuai-C13, iso-C13, tinn-C13, iso-C14, n-C14, ai-C15,iso-C15, n-C15, iso-C16, ai-C17[Ala4]GluLeuLeuAlaAspLeuLeuiso-C14, n-C14, Surfac-ai-C15, iso-C15, tinn-C15[Leu4]GluLeuLeuLeuAspLeuLeu—Surfac-tin[Ile4]GluLeuLeuIleAspLeuLeu—Surfac-tin[Val7]GluLeuLeuValAspLeuValai-C13, iso-C14, Surfac-n-C14, ai-C15tin[Ile7]GluLeuLeuValAspLeuIleai-C13, iso-C13, Surfac-iso-C14, n-C14, tinai-C15, iso-C15Haloba-GlnLeuLeuValAspLeuIle—cillin(lichen-ysins)Underlined amino acids represent D-enantiomers.
The surfactin family members were originally isolated as substances each having a potent surface-active ability. However, research in recent years has revealed that the surfactin family members play important roles in biocontrol activity of the Bacillus sp. bacteria (e.g., involvement in bacterial colonization of a plant and induction of resistance in a plant) (Non Patent Literatures 25 and 26). However, no report has heretofore been made of an interaction (synergistic effect) between prumycin and a surfactin family member.